Cartons or boxes are typically delivered to the user flat and formed with fold lines that permit them easily to be erected into the desired rectangularly parallepipedal shape. In a standard box-erecting apparatus the flat boxes are held in a stack in a magazine from which they are pulled one at a time by a suction grab. An unfolder engages another panel of the box and erects it, and the erected box is deposited in a respective cell of a conveyor that itself comprises a top rail, a bottom rail, and a succession of cell-defining elements that move along between and parallel to the rails. A filling apparatus down-stream of the box-erecting system loads the necessary contents into the boxes in the cells, and other devices may be provided to fold in end flaps and seal the boxes.
As described in German patent document 2,923,909 filed June 13, 1979 by Otto Weller such an apparatus has a support wheel for the grab and for the unfolder. A parallelogrammatic linkage carries these elements so that even though the wheel moves continuously, the grab's angular movement can be temporarily canceled out for the necessary pickup transfer during which the grab effectively is moved only radially inward on the wheel. Once picked up the box is brought up to the peripheral speed of the wheel as it is erected and is then passed off to the conveyor whose transport speed is equal to the wheel's peripheral speed. Once the erected box is set in its cell in the conveyor, the suction grab releases it and this grab retracts radially back into the wheel, out of the way, while the unfolder is moved back to its starting position.
In this arrangement the box is handed by the wheel off to the conveyor before it is fully erected, that is with adjacent panels perfectly perpendicular to each other, because otherwise parts of the unfolder would bump parts of the conveyor. The last stage of the unfolding operation is therefore carried out by the conveyor. As a result exact positioning of the box is impossible and the box will tend by its own elasticity to return somewhat to the flattened condition. The faster the downstream equipment operates, the more this inexactitude is a problem.